docs: def combine_reports(original, new):
      """Combines two gcov reports for a file into one by adding the number of hits on each line
      """
      if original is None:
          return new
      report = {}
      report['name'] = original['name']
      report['source_digest'] = original['source_digest']
      coverage = []
      for original_num, new_num in zip(original['coverage'], new['coverage']):
          if original_num is None:
              coverage.append(new_num)
          elif new_num is None:
              coverage.append(original_num)
          else:
              coverage.append(original_num + new_num)
  
      report['coverage'] = coverage
      return report